Smart windows are designed to reduce the cost of heating, air conditioning and/or lighting. Issues with levels of transmission, haze, degradation over time, and/or high material and processing costs have limited the use of these windows to date.
Thermochromic windows reduce energy costs by transforming from a transmitting state while at low temperature to a reflecting state at high temperatures while substantially maintaining significant visible transmittance, Vanadium Dioxide (VO2) nanoparticles transition from (i) an insulating, monoclinic form VO2(M), while at low temperatures, to (ii) a metallic or substantially metallic, rutile form VO2(R) at high temperatures. Because this metal-to-insulator transition is reversible and occurs near room temperature, VO2 nanoparticles could be used in films on glass for smart windows.
VO2 nanoparticles, however, are highly reactive. The chemical instability of VO2 nanoparticles limits their use in mass production environments. In particular, VO2 nanoparticles have been found to fail under acidic conditions and to oxidize to V2O5 in dry air.
In a related art method, coating VO2 nanoparticles with a silicon dioxide (SiO2) shell was found to significantly improve the anti-oxidation and acid resisting properties of VO2. See Gao, Y., et al., “Enhanced chemical stability of VO2 nanoparticles by the formation of SiO2/VO2 core/shell structures and the application to transparent and flexible VO2-based composite foils with excellent thermochromic properties for solar heat control,” Energy Environ. Sci., 2012, 5, 6104-6110;
However, this related art fails to disclose a thermochromic window using VO2 nanoparticles in a SiO2 shell which is scalable to accommodate large-area production. See Wray, P., “VO2 foils eyed for mass production for thermochromic window applications,” Ceramic Tech Today, Feb. 7, 2012, wherein Yanfeng Gao, the paper's lead author, “says scaling the group's technique to large-area production is the next challenge.” Additionally, there is a need for a thermochromic window, and method of manufacturing the same, which provides good energy efficiency and/or visible transmittance, and/or lowers the manufacturing cost, of thermochromic windows.